The present disclosure relates generally to a high speed semi-hermetically-sealed induction motor that directly drives the centrifugal compressor of a chiller assembly. Some centrifugal compressors utilize medium pressure (MP) refrigerant, magnetic bearings, and a high speed permanent magnet motor. However, high speed permanent magnet motors often require the use of expensive rare-earth materials and a specialized variable speed drive (VSD). Impellers used with medium pressure refrigerants tend to operate at high speeds in order to achieve the required pressure rise. Utilizing low pressure (LP) refrigerant allows for the use of larger diameter impellers and, subsequently, slower operating speeds. The lower operating speed of a LP centrifugal compressor can permit the use of high-speed direct drive induction motors and a simplified VSD. The combination of induction motor technology and simplified VSDs can provide similar performance to permanent magnet motors at a reduced cost.